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Biomedical subjects

G Wollenek

Publications and source records attributed to G Wollenek.

At least 73 records · Page 4Linked to original sources
PubMed1989

Laser angioplasty in the treatment of peripheral vascular disease.

Compared with percutaneous transluminal angioplasty (PTA), the ablation of atherosclerotic tissue by laser energy promises advantages in the treatment of atherosclerotic vascular disease in the peripheral arteries. In the last few years, the basic clinical feasibility has been demonstrated. By development of different lasers and light transmitting devices even the safety of laser energy applied intraluminally has been improved, but to date, no gold standard of laser angioplasty has been defined. Many technological hurdles are still to be overcome and some specific laser-associated problems, especially the high incidence of perforations, has to be resolved before routine application is possible. The future of lasers in vascular diseases seems promising, but there is still a long way to go before reaching maturation.

Angioplasty, Balloon↗
PubMed1989

Independent risk factors predicting acute graft rejection in cardiac transplant recipients treated by triple drug immunosuppression.

To assess independent risk factors predicting the occurrence of clinically significant acute rejection episodes in the first 6 months after cardiac transplantation, we performed a multivariate stepwise logistic regression analysis. Forty-three recipients, undergoing transplantation between September 1986 and May 1988, were eligible for analysis and received standardized, low-dose triple drug maintenance immunosuppression with cyclosporine, azathioprine, and prednisolone. Immunoprophylaxis was supplemented perioperatively with either a polyclonal (antithymocyte globulin, N = 26) or a monoclonal (OKT3, N = 17) anti-T-cell antibody. Investigated, conceivable risk factors comprised recipient and donor age, ischemic time, perioperative anti-T-cell antibody prophylaxis, recipient preoperative status, underlying disease, previous cardiac operation, and histocompatibility parameter (mismatches for HLA-A, HLA-B, HLA-DR, HLA-B+DR, HLA-A+B+DR, and Rh0[D] antigen, HLA-DRw6 positive recipient, and identify for ABO system). Univariate analysis suggested significant influence of the type of antibody used perioperatively (p = 0.0024) and the number of mismatches for HLA-A+B+DR (p = 0.0037) and for HLA-B+DR (p = 0.0043). Stepwise logistic regression yielded the number of mismatches for HLA-B+DR (p = 0.0029) and the type of antibody used perioperatively (p = 0.0031) as being highly significant predictors of acute cardiac rejection. Six-month freedom from rejection was 100%, 41%, and 27% for recipients with two, three, and four mismatches for HLA-B+DR and 59% versus 22% for recipients with polyclonal versus monoclonal antibody prophylaxis. Similar to results with kidney transplantation, these results indicate that a poor donor/recipient match for combined HLA-B+DR loci constitutes an independent risk factor for acute graft rejection in low-dose triple drug immunosuppressed cardiac recipients, which stimulates the potential concept of prospective HLA matching. In our experience OKT3 prophylaxis provides significantly less effective prevention of acute rejection than a comparable course of antithymocyte globulin.

Acute Disease↗
PubMed1988

Percutaneous transluminal excimer laser angioplasty in total peripheral artery occlusion in man.

Laser angioplasty and laser-assisted angioplasty have become a clinical reality. Producing sharply defined borders of the ablated area with minimal adjacent thermal damage, excimer lasers offer several proven and some potential advantages over conventional systems. To evaluate the feasibility of excimer laser angioplasty, we have treated one patient using 308-nm radiation via a bare fiber in direct contact with the total occlusion of a right femoral artery. The lesion was successfully recanalized, thus allowing easy passage of the balloon catheter and subsequent dilatation. This percutaneous laser recanalization of an occluded peripheral artery is one of the first to be done in man using excimer laser radiation, thus demonstrating that the technique is feasible and the system is potentially useful.

Angioplasty, Balloon↗
PubMed1988

Results of orthotopic heart transplantation with and without the use of maintenance steroids.

From March 1984 to June 1987, 51 patients underwent primary orthotopic heart transplantation at the Second University Department of Surgery, Vienna. Recipients were immunosuppressed with a combination of either ciclosporine and azathioprin (double drug regimen = DD, 10 patients), or ciclosporine, azathioprin and low-dose steroids (triple drug regimen = TD, 33 patients). Four patients who died intra- or perioperatively and 4 who were switched to conventional therapy were excluded from analysis. In both groups, ciclosporine was administered to obtain whole blood HPLC trough levels of 200-400 ng/ml in the 1st month, 150-250 ng/ml from the 2nd to the 6th and 100-150 ng/ml after the 6th month. Azathioprin 2 mg/kg per day was given, and in TD patients, an additional 0.2 mg/kg per day of prednisolon: all patients received prophylactic antithymocyte globulin for 7-10 days postoperatively. Five deaths from acute rejection in the DD group contrasted with none in the TD group. The high incidence of fatal rejection episodes was reflected in a 40% Kaplan-Meier 1-year survival for DD vs 84% for TD (p less than 0.0001). Analysis of endomyocardial biopsies (DD vs TD) demonstrated 20.4% vs 57.0% absent, 46.0% vs 29.5% mild, 31.2% vs 12.4% moderate and 2.4% vs 1.1% severe rejection. Fatal and nonfatal infections and toxic side effects occurred with the same frequency in both protocols. Calculation of mean ciclosporine levels resulted in 249.7 ng/ml (TD) and 206.0 ng/ml (DD) in the 1st month (p less than 0.05). Consequently, adjunctive maintenance low-dose steroids combined with increased ciclosporine levels in the early posttransplant course are considered responsible for the improved results.

Azathioprine↗
PubMed1988

Incidence and severity of acute cardiac allograft rejection with two different low-dose cyclosporine maintenance protocols.

Currently cyclosporine (CyA) represents the main immunosuppressive agent used after cardiac transplantation and usually is administered in combination with prednisone and/or azathioprine for prevention of graft rejection. From March, 1984, to August, 1987, 53 patients underwent orthotopic heart transplantation for terminal-stage heart disease at the Second Department of Surgery, University of Vienna. All patients received CyA in increasing dosage (3 mg/kg to 6-10 mg/kg) postoperatively according to renal function, obtaining a trough high-pressure liquid chromatographic whole-blood target level of 200 to 400 ng/ml at the end of the first week. CyA was subsequently tapered to 100 to 150 ng/ml after 6 months. From March, 1984, through April, 1986, maintenance immunosuppression was carried out with a double-drug regimen of CyA and azathioprine. Since May, 1986, a triple-drug schedule was applied with CyA, azathioprine, and prednisone. Under triple-drug therapy, the incidence of mild, moderate (p less than 0.0001), and severe (p = 0.05) allograft rejection proven by endomyocardial biopsy decreased significantly with a corresponding increase of absent (p less than 0.0001) rejection. Freedom from moderate, severe, and lethal graft rejection, number of rejection episodes per patient after 1 year (double drug, 1.0, versus triple drug, 2.5), and patient survival disclosed significant improvement for recipients of the triple-drug regimen. Both groups had the same incidence of infectious complications; freedom from death by infection after 1 year was 90% versus 91% (double versus triple drug, p = 0.20).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1988

Comparative study of different laser systems with special regard to angioplasty.

Laser angioplasty has found increasing interest in the treatment of cardiovascular diseases. First clinical applications of laser angioplasty in atherosclerotic stenoses or occlusions of peripheral and coronary vessels primarily showed a high success rate, but later were followed by significant complications as aneurysm formation, late perforations and restenoses. Most of these complications were due to a thermal damage of surrounding wall structures. To avoid these complications an ideal laser system should only minimally influence surrounding tissue layers and should offer a well predictable penetration and ablation including also severely calcified material. In conventional continuous wave laser systems photo energy is mainly changed into thermal energy. Mode of application, local cooling and the use of special laser probes can reduce the thermal side effects, but nevertheless histologic examinations revealed thermal injuries of various degree to surrounding structures. Furthermore these laser systems mostly faile to ablate or penetrate calcified plaques and only pulsed Nd:YAG-lasers with high frequencies seem ot offer some improvement. Eximer lasers with their wave lengths of 193, 248 and 308 nanometers also work in a high frequent pulsed mode. They offer a very low penetration and mainly show a so called photoablative effect with only minimal thermal side effects. Within a distance of only 50 micrometers temperature raises in the surrounding tissue up to 5 degrees C and in a distance of 1 mm, up to 1.5 degrees C. Eximer lasers are moreover able to penetrate calcified material. A transluminal application is up till now limited by a lack of flexible fiber systems, which can deliver the high energy pulses. Another point of discussion are the mutagenity and cancerogenity of ultraviolet light.(ABSTRACT TRUNCATED AT 250 WORDS)

Angioplasty, Balloon↗
PubMed1988

Excimer laser-induced simultaneous ablation and spectral identification of normal and atherosclerotic arterial tissue layers.

A krypton-fluorine excimer laser at a 248-nm wavelength was used to irradiate normal and severely atherosclerotic segments of human postmortem femoral arteries. Single pulses and multiple pulses required for penetration or perforation of the arterial wall were applied with 16 nsec pulse width and 5 J/cm2/pulse energy fluence. The total fluorescence of irradiated and ablated tissue was analyzed in real-time mode by means of spectroscopy. Each laser pulse produced one spectrum that was characteristic of the composition of the tissue layer, which was ablated. Fluorescence spectroscopy indicated a broad-continuum emission between 300 and 700 nm with peak fluorescence of equal intensity at wavelengths of 370 and 460 nm (ratio, 1.004 +/- 0.087) for normal media layers. Atheromas without calcification (lipid, fibrous, and mixed) were found with spectral maxima at the same wavelengths but with significantly reduced intensity at 460 nm (ratio, 1.765 +/- 0.263; p less than 0.001). In contrast to this broad-continuum fluorescence, calcified plaques displayed multiple-line emission with the most prominent peaks at wavelengths of 397, 442, 450, 461, 528, and 558 nm. These fluorescence criteria identified the histologically classified target tissue precisely. Histological examination of the corresponding arterial layers indicated sharply delineated and circumscribed tissue ablation. These results indicate that simultaneous tissue identification (diagnosis) and ablation (treatment) by excimer laser irradiation is feasible under strict laboratory conditions. We conclude that this principle demonstrates the potential for laser beam control by means of target-specific ablation.

Angioplasty, Balloon↗
PubMed1988

Whole blood aggregometry and platelet adenine nucleotides during cardiac surgery.

The influence of extracorporeal circulation (ECC) on human platelet adenine nucleotides has been studied in 28 coronary bypass patients before, during and after operation. An oscillating pattern of transient increases and decreases in total platelet ATP was observed following the sternotomy until the end of the operation. A highly significant increase in platelet ATP (20% +/- 14 of the pre-anaesthesia values) occurred during the first 24 h after surgery. Total platelet ADP however, did not show this oscillation nor was there any significant release of ADP from the platelets during ECC. Following collagen activation, increased amounts of 'releaseable ATP' were found after protaminization (124% +/- 38 of pre-anaesthesia values) (p less than 0.05), although whole blood aggregability was slightly reduced (89% +/- 18 of pre-anaesthesia values). This study indicates that 1) the metabolic ATP pool of circulating platelets underwent rapid changes during open heart surgery; 2) the majority of platelets did not release inert ADP during ECC; 3) there may be a compensatory enhancement of platelet function by other blood cells, which could explain the discrepancy between our aggregatory results in whole blood and those reported in platelet rich plasma (PRP) aggregometry.

Adenosine Diphosphate↗
PubMed1987

Scanning electron microscopy of circulating platelets reveals new aspects of platelet alteration during cardiopulmonary bypass operations.

Seventeen male patients undergoing cardiopulmonary bypass (CPBP) surgery for aorto-coronary bypass grafting were investigated by scanning electron microscopy (SEM) for alterations of the surface morphology of circulating platelets. An initial decline in the percentage of unactivated smooth discocytes (SD) to 87 +/- 12% was found after thoracotomy. Three minutes after the onset of CPBP, the percentage of SD had dropped drastically to 59 +/- 13%, and by the 8th minute of CPBP it had dropped to its lowest point (49 +/- 19%). On the other hand, the percentage of shape-changed platelets (SC) increased to 17 +/- 9% after 3 minutes, and the percentage of pseudopod discocytes (PD) to 25 +/- 13% after 8 minutes. Surprisingly, a remarkable recovery of platelet morphology could be observed after even 15 minutes of CPBP, and by the end of bypass 78 +/- 15% of the circulating platelets had regained the smooth discoid (SD) appearance of unactivated platelets. We conclude that this recovery of platelet morphology is due to an increasing insensitivity of the platelets to activating stimuli during the course of CPBP. Our study provides evidence that the only major platelet activation occurs during the first minutes of CPBP, and that CPBP-caused platelet activation is much less pronounced than generally believed.

Journal Article↗
PubMed1987

Plaque ablation by excimer laser irradiation using a movable energy-transmitting device.

During the past 2 years, excimer laser energy has been shown to provide a highly suitable type of atherosclerotic plaque ablation, especially in small-diameter vessels such as coronary or crural arteries. Nevertheless, transmission of far-ultraviolet pulsed laser power has remained a major problem in animal studies and clinical trials. In an attempt to solve this problem, we constructed an energy-transmitting device for use with a Lambdaphysics EMG 102 excimer laser. The transmission system, which was housed in a rigid articulated arm, allowed movement in all directions and rotation along the long axis, thus permitting easy handling and guiding of the laser beam in the operating field. To test whether this device could deliver enough energy to remove atherosclerotic plaques within a period that would meet the requirements for intraoperative use, we obtained fresh human cadaver coronary arteries both with and without atherosclerotic disease, and irradiated them vertically and coaxially. A power meter was used to determine the effective amount of energy delivered at the distal end of each vessel. Energy densities up to 3 J/cm(2)/pulse were obtained, owing to energy focussing within the transmitting device. At 5 Hertz (Hz), tissue ablation consisted of approximately 20 microm/pulse. Areas of normal vascular tissue, as well as fibrohyalinous and lipid plaque components, were promptly ablated. Macroscopically, the "lasered holes" appeared well-circumscribed, with clear-cut surfaces and no carbonization. Light microscopy revealed no thermal damage to the boundary tissue. With this new energy-transmitting device, the surgeon can use excimer laser irradiation intraoperatively. There is no significant loss of energy between the generator and the tip, and energy densities of 3 J/cm(2)/pulse are available for sufficient plaque removal.

Journal Article↗
PubMed1986

Laser-induced vascular lesions by cw-NdYAG or pulsed UV lasers during angioplastic procedures.

Conventional (NdYAG, Argon and CO2 lasers) laser and pulsed far ultraviolet laser radiation are able to remove arteriosclerotic tissue of the arterial wall. However, there is a striking difference between both systems: The continuous wave of conventional wave-length laser-radiation produces considerable thermal injury to the surrounding tissue, whereas the effect of pulsed far ultraviolet radiation induces less or no thermal damage despite an easily assessable tissue-removing effect. In the following study the potential of far UV laser-radiation for recanalization of occluded vessels is demonstrated in in-vitro experiments on fresh and well preserved atherosclerotic human vessels.

Animals↗
PubMed1985

[Qualitative and quantitative effects of neodymium YAG laser irradiation of the aortas of swine with reference to angioplasty].

During last few years the concept of vaporizing atheromatous plaques and thrombotic occlusions by laser energy arose. This method is a new and possibly valuable modality in the treatment of obstructive vascular diseases. We used a continuous 1,060 nm Nd-YAG laser with a focused optical wave guide. Sections of porcine aortic vessels were split longitudinally and exposed to laser radiation. Four major types of tissue alterations were observed: local swelling, disruption of the inner layers of the vessel wall, charred punched-out defects and wall perforation. Histologic examination revealed a typical damage pattern as a result of thermic injury. Clean tissue alteration is the desired effect for angioplasty. The thermic alterations limit the applicability when dealing with the cw Nd-YAG laser for this purpose.

Animals↗
PubMed1985

Experimental coronary angioplasty using a UV-Excimer laser.

Both conventional Argon- and NdYAG-lasers in continuous wave or pulsed application and far ultraviolet laser radiation are able to cause a loss of substance of biologic tissue. The thermic and ablative effects of NdYAG-lasers and UV-Excimer lasers at the wavelengths of 193 nm (ArF) and 248 mm (KrF) on inconspicuous and atherosclerotic human and animal coronary vessels were compared by histologic and, in some cases, by scanning electron microscopic examinations. Whereas common lasers generally produce thermal injuries of the surroundings, pulsed far ultra-violet radiation is characterized by a lack of thermic damage. The UV-radiation in vitro cleaned precise defects of substance, and assessable tissue-removing effects were found. These results were influenced by the wavelength used. In general, the removing effect was good in normal and atherosclerotic tissue, whereas massive calcification was very resistant. Excimer lasers seem to be preferable for ablation of atherosclerotic tissue, but still there is a great number of technical problems to be solved until use in the clinical setting can be justified.

Journal Article↗
PubMed1985

[Coronary laser angioplasty].

Experimental studies have confirmed the feasibility of removing thrombotic material and atheromatous plaques with laser energy. Secondary to the heat generated at the site of conventional, continuous-wave laser radiation, thermic lesions of the vascular wall can be observed as adverse reactions. In the clinical setting, these lesions could prove to be of substantial potential danger. The energy emitted from the excimer laser, in the lower UV range, does not result in thermic damage. The luminal widening rendered is well delineated and the newly-created surfaces are relatively smooth. The extent of ablation is highly predictable. Problems dealing with transmissions of the UV laser energy remain to be solved. Nevertheless, high-energy, pulsed NdYAG- or argon laser systems, at least for medium-term periods, would appear to represent a useful alternative.

Angioplasty, Balloon↗